As of March 27, 2015, there have been five Cumulative Updates (CU) for the Service Pack 2 branch of SQL Server 2012. There have been a fairly high number of hotfixes in every one of these Cumulative Updates, as more people are using SQL Server 2012. If you are running SQL Server 2012, I really think you should be running the latest SQL Server 2012 Service Pack and Cumulative Update. Right now, that means Service Pack 2, CU5 (Build 11.0.5582), which was released on March 16, 2015.
If you are still on the SQL Server 2012 SP1 branch, then you want to be on SP1 CU15. But really, you should be on the SP2 branch as soon as possible. Table 1 shows the SQL Server 2012 SP2 CU builds that have been released so far.
|11.0.5058||SP2 RTM||June 10, 2014|
|11.0.5532||SP2 CU1||July 23, 2014|
|11.0.5548||SP2 CU2||September 15, 2014|
|11.0.5556||SP2 CU3||November 17, 2014|
|11.0.5569||SP2 CU4||January 19, 2015|
|11.0.5582||SP2 CU5||March 16, 2015|
Table 1: SQL Server 2012 SP2 CU Builds
You can follow the KB article link below to see all of the CU builds for the SQL Server 2012 Service Pack 2 branch.
Like I did for the SQL Server 2012 SP1 branch, I decided to scan the hotfix list for all of the Cumulative Updates in the SP2 branch, looking for performance and general reliability-related fixes for the SQL Server Database Engine. I came up with the list below, but this listing is completely arbitrary on my part. You may come up with a completely different list, based on what specific SQL Server 2012 features you are using.
Here are the fixes in the Service Pack 1 branch:
SQL Server 2012 SP2 Cumulative Update 1 (Build 11.0.5532), 43 total public hot fixes
SQL Server 2012 SP2 Cumulative Update 2 (Build 11.0.5548), 43 total public hot fixes
SQL Server 2012 SP2 Cumulative Update 3 (Build 11.0.5556), 32 total public hot fixes
SQL Server 2012 SP2 Cumulative Update 4 (Build 11.0.5569), 36 total public hot fixes
SQL Server 2012 SP2 Cumulative Update 5 (Build 11.0.5582), 27 total public hot fixes
Once again, the idea here is to give you a lot of concrete reasons to want to stay current with the latest SQL Server 2012 SP and CU, by pointing out some of the more valuable fixes in each CU in the Service Pack 2 branch. If my opinion does not sway everyone, this relatively new Microsoft KB article might be more convincing:
Happily, Microsoft has been updating this KB article with new information, so you might want to read it again, if you have not done so already.